1. Field of the Invention
The present invention generally relates to an Internet Protocol version 6 over Low power Wireless Personal Area Network (6LoWPAN) for transmitting an IPv6 packet over an Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 network. More particularly, the present invention relates to a method and apparatus for providing a gateway for IPv6 packet transmission in a Wireless Local Area Network (WLAN) system, for simplifying the protocol stack of a 6LoWPAN node.
2. Description of the Related Art
Recently, 6LowPAN has attracted a great deal of interest, as manufacturers see a market with large potential for growth.
FIG. 1 illustrates a network configuration in which a 6LoWPAN protocol stack is applied to a conventional IEEE 802.15.4 network. Referring to FIG. 1, in a 6LoWPAN network, a 6LoWPAN host 112, a 6LoWPAN node 114, and a host 110 within an external IP network are interconnected, so that wireless personal communications or data communications with the external network can occur. In the 6LoWPAN network, one of a plurality of 6LoWPAN nodes connected to the IEEE 802.15.4 network serves as a host and performs a TCP/IP communication protocol by 6LoWPAN network processing. Hence, the 6LoWPAN host 112 allocates IPv6 addresses to a plurality of 6LoWPAN nodes connected thereto, so that the 6LoWPAN nodes can exchange data with the host 110 within the external IP network. As IPv6 usually uses a 126-bit address system, the use of these addresses in a sensor network enables IP allocation to each sensor node.
Hence, conventional communication protocols for the Internet, such as IPv6 and TCP/UDP, can be used as higher layers above IEEE 802.15.4 Medium Access Control/Physical (MAC/PHY) layers. Since an IPv6 address is allocated to each sensor node in the 6LoWPAN network, data communication is possible between a 6LoWPAN node and the host within the external IP network and the 6LoWPAN host within the 6LoWPAN network can control each sensor node.
The IEEE 802.15.4 network uses a physical packet of up to 127 bytes and a MAC frame of 102 bytes. However, up to 1280 bytes can be transmitted in IPv6. This means that the 6LoWPAN network should fragment packets. For a maximum transmission traffic amount in the 6LoWPAN network, considering a physical packet size of 127 bytes, a maximum overhead per frame of 15 bytes, and a link layer security overhead, only 81-bytes of data can be transmitted in the IEEE 802.15.4 network. Since the header of an IPv6 packet is 40 bytes, 41 bytes are available, but a User Datagram Protocol (UDP) header occupies 8 bytes. Thus, in actuality, only 33 bytes are available, and the result is that header compression is required.
Packet fragmentation and the header compression take place in an adaptation layer of the communication protocol stack of the 6LoWPAN host 112. The TCP/IP stack responsible for the packet fragmentation and the header compression is already designed in a legacy host. Hence, the 6LoWPAN host 112 fragments a packet and compresses a header in a TCP/IP layer, thereby increasing power consumption and decreasing the lifetime of the 6LoWPAN node. This is against the development trend of 6LoWPAN nodes toward low power, small size, and small memory.
Moreover, because all operations based on network processing, including TCP SYN, ACK, and ICMP packets (ping, unreachable packet), are carried out in 6LoWPAN nodes, traffic increases between the 6LoWPAN network and the IEEE 802.15.4 wireless network.
Accordingly, the following IPv6 packet headers should be delivered uncompressed between the 6LoWPAN node 112 and the 6LoWPAN node 114 in the 6LoWPAN network, thus increasing overhead.                HOP-by-HOP Options Header        Routing Header        Fragment Header        Destination Options Header        
Although more advanced network technologies are required along with the increased performance of a 6LoWPAN network system aiming at low power and small size, the existence of a TCP/IP protocol stack for packet transmission in a legacy 6LoWPAN host and a small-size memory leads to a traffic increase between networks and a load increase in 6LoWPAN nodes. As a consequence, reliable data communications are not guaranteed.